1. Field of the Invention
This invention relates to an axial flow fluid machine and more particularly to an internal construction or diaphragm of a stage in a steam turbine, gas turbine, compressor and so on.
2. Description of the Prior Art
Stationary blades and rotary blades used in ordinary axial flow fluid machines, particularly in high and intermediate stages of steam turbines and in gas turbine stages, have a small aspect ratio (blade chord/blade height). In axial flow turbines, there are various kinds of losses, such as a blade profile loss, a secondary flow loss and a tip clearance leakage loss. In the turbine stages provided with the blades having a small aspect ratio, the secondary flow loss is greatly increased in comparison with the other losses. The secondary flow loss is caused by the interference of the flow in the blade lattice with the boundary layers developed on the inner and outer wall surfaces of the diaphragm, and there have, therefore, been proposed some methods for reducing the secondary flow loss, such as (1) a method for controlling the vortex flow, (2) a method for adjusting the blade inclination and (3) a method for converging the inner and outer walls. However, none of these methods is a definitive expedient for reducing the secondary flow loss, because there practical difficulties in the alternation of the blade configuration and the blade assembly and the working of the walls.